Sulfur dehydrogenation of organic compounds



United States Patent 3,456,026 SULFUR DEHYDROGENATION OF ORGANIC COMPOUNDS Abraham David Cohen, Sarnia, Ontario, Canada, assignor to Esso Research and Engineering Company, a corporation of Delaware N0 Drawing. Filed Nov. 1, 1967, Ser. No. 679,667 Int. Cl. C07c /20 U.S. Cl. 260-669 17 Claims ABSTRACT OF THE DISCLOSURE Vapor phase dehydrogenation of organic compounds is effected with sulfur in the presence of an inert gaseous diluent which serves to lower the partial pressure of the reactants; the reaction can be effected with or without a catalyst, such catalysts as low surface area support materials with or without additional catalytic agents being useful.

The invention relates to the vapor phase dehydrogenation of organic compounds. More particularly, this invention relates to a process for effecting the dehydrogenation of hydrocarbon by reaction with sulfur in the presence of an inert diluent. In a preferred embodiment, the invention relates to a catalytic process, wherein the yield of unsaturated products may be substantially enhanced.

The dehydrogenation of organic compounds to produce unsaturated or more highly unsaturated products in the presence of sulfur has long been known inthe art. An early reference, US. 1,997,967, discloses the use of small amounts of sulfur, e.g. about 6% by weight, with or without inert gases, in the preparation of styrene from ethyl benzene. However, the yields of styrene were rather low, eg about 46%, and conversions and selectivities were also low. Other vapor phase processes have since been developed, one of the more recent processes being disclosed in US. 3,110,741. However, the product yield here was also quite low, e.g. about 55%, and the reaction was not effected in the present of an inert diluent.

By the process of this invention, however, unsaturated products may be prepared in high yields by dehydrogenation of hydrocarbon materials. The major problem of the prior art, and responsible for the low yields, was thought to be undesirable side reactions resulting in tar formation and the burning of hydrocarbons to carbon disulfide and hydrogen sulfide.

It has now been discovered that the effect of these undesirable side reactions may be substantially reduced, thereby substantially increasing the yield of dehydrogenated product by introducing the reactants to the reaction zone at a low partial pressure. Thus, high yields of unsaturated products may be obtained by reacting an organic compound with sulfur in the vapor phase wherein the partial pressure of the sulfur in the vapor phase wherein the partial pressure of the sulfur has been reduced by the addition of an inert diluent. In a preferred embodiment of this invention a catalyst is employed to substantially increase the conversion of the organic compound, thereby increasing the overall yield of unsaturated product.

The use of inert diluents in oXidative dehydrogenation reactions is well known, e.g. U.S. 3,210,436. However, the use of such diluents has been directed towards the removal of heat in these exothermic reaction systems. The wellknown halogen promoted oxidative dehydrogenation systems as well as sufur promoted oxidative dehydrogenation systems utilize inert diluents to absorb the heat of reaction and thereby maintain, as nearly as possible, isothermal reaction conditions so that burning of the hydrocarbon feed to CO CO and H 0 is minimized. However, the present invention does not utilize oxygen but utilizes sulfur only ice and is, therefore, an endothermic dehydrogenation reaction. Consequently, the function of the inert diluent is not to provide a better control of an exotherim reaction, but to increase the rate of the dehydrogenation reaction relative to the rate of the undesirable side reactions.

While not desirous of being bound to-any particular theory it is believed that there are two major reasons for the increase in the rate of the sulfur dehydrogenation reaction as the partial pressure of the reactants is decreased. Firstly, within the temperature range of this invention lowering the partial pressure of sulfur vapor causes sulfur species of the form S (where n 2 and the sulfur is normally bound in ring structures) to dissociate to give S It is believed that S is the active sulfur species since the hydrogen abstraction ability of S is greater than the ring forms of S molecules. For example, calculations indicate that the reaction:

is only about 20 kcaL/more endothermic while the reaction:

is about 45 kcal./ mole endothermic. The significantly lower endothermicity of reaction (1) shows the greater efficacy of S as a dehydrogenation agent. Secondly, the overall sulfur dehydrogenation reaction involving S and the hydrocarbon feed always produce more molecules in the product than were originally present. For example in the balanced equation:

three molecules of reactants become four molecules of products. Thus, the driving force for this class of reactions increases as the partial pressure of the reactants is decreased. Therefore, lowering the partial pressure of the reactants in the sulfur dehydrogenation of organic feeds must increase the driving force and, therefore, the velocity of the reaction.

The process of this invention can be applied to a great variety of organic compounds to obtain the unsaturated derivatives thereof. Generally, such compounds will contain about 2-20 carbon atoms and have at least one l grouping, i.e., adjacent carbon atoms singly bonded to each other and each attached to at least one hydrogen atom. In addition to carbon and hydrogen, these compounds may also contain oxygen, halogens, nitrogen, and sulfur. Among the classes of organic compounds which can be dehydrogenated by this process are: alkanes, alkenes, alkyl halides, ethers, esters, aldehydes, ketones, organic acids, alkyl aromatic compounds, alkyl heterocyclics, cyanoalkanes, cyanoalkenes, and the like. Illustrative applications include: ethylbenzene to styrene, isopropyl benzene to ot-methyl styrene, cyclohexane to benzene, ethane to ethylene, n-butane to butenes and butadiene, isobutane to isobutylene, methyl butene to isoprene, propionaldehyde to acrolein, ethyl chloride to vinyl chloride, propionitrile to acrylonitrile, methyl isobutyrate to methyl methacrylate, propionic acid to acrylic acid, ethyl pyridine to vinyl pyridine, and the like. Preferred feedstocks are the C -C hydrocarbons, i.e., paraflins, alkyl benzenes, and monoolefins. Particularly preferred, however, are C to C parafiins, C to C monoolefins, and C to C alkyl benzenes. Particularly effective as feedstocks are the olefinic hydrocarbons or alkyl benzenes which may be dehydrogenated to provide a product wherein the major unsaturated product has the same number of carbon atoms at the feed hydrocarbon.

The inert gas which may be employed to reduce the partial pressure of the sulfur vapor may be any gas normally inert under the conditions of the reaction. Illustrative of the gases that may be employed are: helium, notrogen, carbon monoxide, carbon dioxide, steam, hydrogen sulfide, etc. as well as methane, waste gases containing methane, and mixtures of the foregoing. The molar ratio of inert diluent to sulfur is not critical and may vary over a wide range as long as at least about two moles of diluent are present. This value, however, is merely an arbitrary limit at which the yield of dehydrogenated product becomes practical and economical. Molar ratios below this value will also show increases in yield, generally the conversion and yield increasing with increased dilution of the sulfur. The upper limit is not at all critical and larger amounts of diluent will only serve to further reduce the sulfur vapor partial pressure. Preferably, however, a molar ratio of 2 to 30, more preferably 6 to 14, of diluent to sulfur is employed.

It will be readily realized by those skilled in the art that the partial pressure of the reactants can be partially or wholly reduced by use of a vacuum so that the inert diluent may be partially or wholly dispensed with, respectively. However, because of practical difiiculties involved, this method is not preferred.

The reaction conditions under which this process is carried out are not critical and may vary widely. Temperatures should be such that the reaction is effected in the vapor phase. Normally, however, temperatures in excess of about 800 F. and preferably ranging from about 8001400 F., more preferably 1050-1300 F., e.g., 1200 F. may be employed. The space velosity of the reaction is normally dependent upon reaction temperature, i.e., higher temperatures corresponding to shorter contact times. However, space velocities usually range from about 0.15 to 1.15 grams per hour of feed per gram of catalyst (w./w./hr.), preferably about 0.30- 0.75 w./w./hr., e.g., 0.50 w./w./hr. Reaction pressures are not critical and may also vary over a wide range. Pressures from less than one atmosphere to about 50 atmospheres, preferably 0.7 to 7 atmospheres, e.g., 1 atmosphere, may be successfully employed in the process.

The molar ratio of sulfur to feed material is dependent upon the degree of unsaturation required in the end product. For example, butane may be dehydrogenated to produce butene or butadiene according to the following equations:

CH -CH CH -CH /2 S2) CH CH=CHCH +H S (1) CH CH=CHCH /2 8 CH CH-CH=CH +H S (2) The sum of these equations yields:

As previously mentioned, the active sulfur is believed to be S Theoretically, therefore, one-half mole of S is necessary to produce one mole of a monounsaturate from a saturated compound. However, it has been found that significant yields may be expected when as little as 0.1 mole of [S per mole of feed is employed. (For convenience, whenever the mole ratio of feed to sulfur is given, the relative sulfur concentration is quoted as if all the sulfur present was only in the molecular form S To indicate that this is an arbitrary nomenclature S is written as [8 Thus, in this process at least about 0.1 moles [S per mole of feed should be employed. However, it is preferable to employ at least about 0.3 mole, and more preferably, about 0.4-1.1 moles, and still more preferably, 0.40.8 mole of [S per mole of feed. When a large excess of sulfur is employed the desired product is substantially degraded into heavy products.

While the process of this invention may be conducted without a catalyst, it is generally preferable, in order to achieve optimum conversion and yields, to employ catalytic agents. Various catalyst systems can be employed herein; however, a crtical requirement of the catalyst is that it not only catalyzes the desired reaction but also inhibits undesirable side reactions such as cracking and/ or tar formation, thereby permitting the most effective use of the hydrocarbon feed. Cracking and/or tar formation may be inhibited by various techniques, such as impregnating large surface area materials with inert materials to effectively reduce the surface area, adjusting catalyst pore sizes, e.g., as in molecular sieves, so as to preclude the admittance of the feedstocks, or preferably, the use of low surface area catalysts. Preferred catalysts are those that are or could be used as catalyst support materials. More specifically, these catalysts may be described as difficulty reducible oxides or refractory oxides which are selected from the oxides of the metals of Groups II, III, IV, V, and VI-B of the Periodic Chart of the Elements, though the oxides of Groups II, III-A, and V-B are preferred. Suitable examples of these oxides are: magnesia, barium oxide, thoria, alumina, boria, alundum, vanadia, chromia, titania, silica, silica-alumina, tungsten oxide, and the like. Of these silica and Group II-B oxides are most preferred, particularly aluminum oxide in its various forms, e.g., alumina, alundum. Additionally, such common supports as silicon carbide; carbon, e.g., coke, activated carbon, graphite; diatomaceous earths, e.g., kieselguhr; clays both natural and synthetic, e.g., attapulgite clays, magnesium silicates; phosphates, e.g., calcium nickel phosphate, aluminum phosphate, calcium aluminum phosphate; and zeolites, etc. may also be employed. Of these latter materials phosphates are generally preferred.

When aluminum oxide is employed as the catalyst, it has been found that its surface area, when measured by nitrogen adsorption, should be in the range of about 0.01 to m. /g., preferably about 0.05 to 20 m. /g., and still more preferably 1 to 12 mf /g. However, the optimum surface area for alumina is not necessarily the same for other materials. Nevertheless, one skilled in the art will readily determine the proper surface area which inhibits cracking and/or tar formation and utilizes the catalyst at peak efficiency. As a general rule, however, lower surface areas reduce cracking and/ or tar formation and, therefore, surface areas should generally be below about 100 m. /g., preferably below about 50 m. /g., more preferably below about 20 m. /g., depending, of course, on the particular support being employed. Additionally, the surface area of high surface area materials may be reduced by any of the techniques mentioned above. However, it is also possible to reduce surface area by heat treating, for example, a 265 m. /g. alumina heated for several hours at about 2000 F., will result in a catalyst of optimum surface area that will give excellent conversions and yields in sulfur dehydrogenation.

Reasonably high conversions and yields can be effected by simply employing the above-disclosed catalysts. Nevertheless, it is often advantageous to utilize an additional catalyst to increase the obtainable conversions. A wide variety of metals, their salts, oxides and hydroxides, preferably the oxides, can be used for this purpose and in fact suitable metals or mixtures of metals can be selected from Group I-A through Group VIII of the Periodic Chart of Elements. Examples of these metals are: potassium, calcium, magnesium, titanium, chromium, manganese, iron, copper, zinc, tin, antimony, cerium, uranium, tungsten and the like. When a support is used, the weight ratio of metal to support may vary from 0.001 to 1.0, preferably from 0.01 to 0.25. The metals or metal compounds are preferably solid at reaction temperatures, but they may be molten, e.g., antimony. Metals such as mercury which are gaseous at reaction temperatures are not suitable and are therefore excluded from use. The metals or metal compounds can be deposited onto the support in any known manner, e.g., impregnation from dilute solutions, etc.

Concerning the methods of carrying out this invention, various methods will be evident to those versed in the art. A typical embodiment of this invention will be given below. It is not intended, however, to limit the invention in any way to a particular method of carrying out the process.

The reactor input consists of two streams: firstly, a stream consisting of inert diluent and sulfur vapor and, secondly, a stream consisting of hydrocarbon feed which may or may not contain inert diluent. Both streams are preheated but the first one is preheated to a higher temperature, e.g., about 300 F. greater, than the second one. The preheating operation is so controlled that when the two gas streams are mixed at the top of the reactor vessel they attain the requisite reaction temperature and their components are in the appropriate mole ratio. (For example, at the top of the reactor the reactants are ethylbenzene, [S and inert gas in the mole ratio 1/0.7/ 8.5 at an average temperature of 1300 F.) The reactor contains a catalyst, which may be utilized in a fixed, fluidized or moving bed, wherein the desired dehydrogenation takes place.

The product stream, which mostly consists of styrene, H 8 and inert diluent (or diluents) together with any unconverted sulfur and ethylbenzene is then rapidly quenched. It is convenient for some or all of the inert diluent to be steam since on cooling the reactor efiluent an aqueous layer would be obtained that would contain most of the unreacted sulfur in colloidal form suitable for recycle to the reactor. The gas eflluent can be treated in a conventional sulfur plant to oxidize the H 8 back to sulfur for recycle to the reactor. The liquid product is subjected to standard distillation procedures now employed in ethylbenzene thermal dehydrogenation units. This allows the separation of styrene from the liquid product, and also recovers unreacted ethylbenzene for recycle to the reactor.

Having now described this invention, a better appreciation of this process will be had from the following illustrative examples. Many variations of this inventive process will be known to those skilled in the art and, therefore, no limitations, expressed or implied, are intended by these examples.

PROCEDURE In all the illustrative examples the reactor feed ethylbenzene and gases were accurately metered by the use of rotameters. The reactor consisted of a 1 inch diameter Vycor tube which could be conveniently filled with a catalyst. The reactor was heated in a temperature controlled furnace to the desired temperature. Part of the reactor served to preheat the sulfur vapor and ethylben zene separately to a temperature near that of the reaction zone of the reactor. The reactor efiluent was rapidly quenched by passing it through a water cooled condenser placed immediately after the reactor. Both the gas and liquid reactor effluent were weighed and then subjected to gas chromatographic analysis. For the thermal dehydrogenation experiments with ethylbenzene the sulfur in the reactor feed was omitted.

Example 1 Table I below gives data for the thermal dehydrogenation of ethylbenzene to styrene with and without a catalyst at various temperatures.

TABLE I.THERMAL DEHYDRO GENATION OF ETHYL- BENZENE EB [He mole ratio= 1/30 Residence timezO. 5 see. Space velocity :0. 2 w./w./hr.

Selec- EB Contivity to Yield of version, Styrene, Styrene, Temp Mole Mole Mole Catalyst percent percent percent 1, 000 o 0 0 1, 100 1. 2 75 0. 9 1, 200 4. 4 79 3. 5 1, 250 11. 7 79 9. 3 1,000 1. 4 s9 1. 2 100 3. o 2. 7 1, 200 10. 7 91. 5 9. 8 250 23. 0 90 20. 6

This table shows the relatively poor conversions achieved with ethylbenzene by thermal dehydrogenation with or Without a catalyst of 4.75 mP/g. surface area alumina.

Example 2 Table 11 below gives data for the sulfur dehydrogenation of ethylbenzene with and without a catalyst.

TABLE II.SULFUR PROMOTED DEHYDROGENATION OF ETHYLBENZENE Mole ratio of EB/[S2]/He=1/0. 5/30 Contact timezO. 5 sec. Space ve1oeity:0.2 w./w./hr.

Selec- EB Contlvity to Yield of version, Styrene, Styrene, Temp e Mole Mole Catalyst percent percent percent 1, 000 s. 4 ss 7. 5 1, 29. 4 85 25 1, 200 25. 6 87. 5 49. 5 1, 250 77. 1 88 68 1, 000 70 87 61 1, 100 87. 7 94 82. 5 1, 200 92. 5 93. 5 85. 2 1, 250 84. 0 78. 6

This table when compared to Table I clearly shows that the addition of sulfur to the feed markedly increases the ethylbenzene conversion and the yield of styrene that may be obtained both with and without a catalyst. Furthermore, this table also clearly shows the advantage of using a catalyst for sulfur dehydrogenation.

Example 3 Table III below gives data on the effect the inert diluent mole ratio to ethylbenzene has on the sulfur dehydrogenation of ethylbenzene to styrene. 1

TABLE TIL-EFFECT OF DILUENI CONCENTRATION ON SULFUR DEHYDROGENATION OF ETHYLBENZENE Mole ratio of [Sfl/EB =0. 5 Temperature=1, F.

This table indicates that ethylbenzene conversion increases with increasing diluent ratios, thus illustrating the beneficial etfect of inert diluent addition, i.e., lowered partial pressure of the feed.

Example 4 Table IV below gives data on the effect of sulfur concentration on the sulfur dehydrogenation of ethylbenzene to styrene.

TABLE IV.EFFECT OF SULPHUR CONCENTRATION Temperature=1, 300 F.

Catalyst: Alumina with a surface area of 0. 04 mfl/g. He/EB, mole ratio=8. 5/1

Contact timezO. 35 see.

Space velocityzO. 6 w.w./hr.

Selec- This table shows that there is an optimum sulfur concentration range for best styrene yield. Under the conditions employed in Table IV the optimum sulfur concentration was about 0.8 mole of [S per mole of ethylbenzene. At higher concentrations of sulfur the product styrene is degraded to heavy products.

Example 5 Table V below gives data of the effect of temperature on sulfur dehydrogenation of ethylbenzene to styrene.

TABLE V.-EFFECT OF TEMPERATURE Catalyst: Alumina with a surface area of 3.7 mfi/g. Contact timezO. 5 sec.

Mole ratio of EB/[S ]/Hez1/0.8/8.5

Space velocity=0. 6 w./w./hr.

Selec- EB Contivity to Yield of version, Styrene, Styrene, Mole Mole Mole percent percent percent Temperature, F.:

Table V shows that there is an optimum temperature range for best styrene yield. Under the conditions employed in Table V the optimum temperature was about 1300 F.

Example 6 Table VI below gives data on different sulfur dehydrogenation catalysts for the conversion of ethylbenzene t0 styrene.

TABLE VL-SOME USEFUL CATALYSTS Mole ratio of EB/[Sz]/He=1/0.5/8.4 Temperature=1,300 F. Space velocityzOfi w./w./hr.

The above table gives some indication of the wide range of catalyst that can be employed in this invention.

8 Example 7 Table VII below gives data on the effect of sulfur addition on the conversion of butene-l to butadiene.

TABLE VII.B UTENE-l TO B UTADIENE Mole ratio of Butenel/He= 1/8.5 Space velocity=0.38 w./w./hr. Catalyst: Alzoa, 5.9 mfl/g. surface area Temperature=l,300 F.

Wt. Percent Conversion Selecof Butene-l tivity to 7 Yield of into Products Butadiene Butadiene Other Than in Wt. in Wt. Butene-2 Percent Percent Mole Ratio of [S2] to Butane-l:

The above table shows that the addition of sulfur markedly increases both the yield of and selectivity to butadiene from butene-l.

Example 8 Table VIII below gives data on the effect of sulfur addition on the conversion of butane to butadiene.

TABLE VIII.B UTANE TO BUIADIENE Butane/He=l/53 Space vclocity=6.6 l0- w./w./hr. Temperature=l,250 F.

Surface Conver- Selec- Area of sion of tivity to Yield of A1203 Butane Butadiene Butadiene Catalyst in Wt in Wt. in Wt. in mfl/g. Percent Percent Percent Mole Ratio of [Sz] to Bu ne:

The above table shows that sulfur addition increases both the yield of and selectivity to butadiene from butane.

What is claimed is:

1. A process for the dehydrogenation of organic feedstocks containing at least one l l grouping which comprises reacting, in the vapor phase, a C C organic feedstock and at least about 0.1 mole [S per mole of feed, the reaction being conducted at a temperature of at least about 800 F., and in the presence of an inert diluent.

2. The process of claim 1 wherein the inert diluent is present in an amount of at least about 2 moles per mole of feed.

3. The process of claim 1 wherein the molar ratio of inert diluent to feed is about 2/1 to 30/1.

4. The process of claim 1 wherein the feed is a hydrocarbon.

5. The process of claim 1 wherein a support material selected from the group consisting of oxides of metals of Groups II, III, IV, V, and VI-B, silicon carbide, carbon, diatomaceous earths, clays, phosphates, and zeolites is employed as a catalyst and has a surface area below about mF/gm. is employed.

6. The process of claim 5 wherein the support is alumina.

7. A process for the dehydrogenation of a C C feed hydrocarbon having at least one H II I l grouping which comprises reacting, in the vapor phase, the feed hydrocarbon with at least about 0.1 moles [S per mole of feed hydrocarbon, at a temperature ranging from about 800 F. to 1400 F., in the presence of at least about 2 moles of inert diluent per mole of feed hydrocarbon, and in the presence of a support material 9 selected from the group consisting of oxides of metals of Groups II, III, IV, V, and VI-B, silicon carbide, carbon, diatomaceous earths, clays, phosphates, and zeolites having a surface area below about 100 m. gm.

8. The process of claim 7 wherein the hydrocarbon feed is selected from the group consisting of C -C paraffins, C C monoolefins, and C C alkyl benzenes.

9. The process of claim 8 wherein the feed is ethyl benzene.

10. The process of claim 7 wherein the temperature ranges from about 1050-1300 F.

11. The process of claim 7 wherein the inert diluent is employed in an amount of 230 moles per mole of feed hydrocarbon.

12. The process of claim 7 wherein the molar ratio of [S to feed is about 0.4/1 to 0.8/1.

13. The process of claim 7 wherein the support material is selected from the group consisting of silica, alumina, and phosphates.

14. The process of claim 7 wherein the support is alumina of a surface area ranging from 0.5 to 20 mF/gm.

15. The process of claim 7 wherein the support is a phosphate.

16. The process of claim 7 wherein the support is silica.

17. The process of claim 7 wherein the catalyst is selected from the group consisting of oxides of metals of Group II, III, IV, V, and VIB.

References Cited UNITED STATES PATENTS 2,392,289 1/1946 McCullough et al. 260669 3,247,278 4/1966 Garwood et a1. 260683.3 3,344,201 9/1967 Schuman 260669 3,373,213 3/1968 Pasternak et al. 260683.3 XR 3,387,054 6/1968 Schuman 260-680 DELBERT E. GANTZ, Primary Examiner CURTIS R. DAVIS, Assistant Examiner US. Cl. X.R. 260680, 683.3 

